The goal of this proposal is the development of a method for early detection, quantification and grading of atherosclerosis in arteries particularly before the appearance of clinical signs of ischemia due to far advanced lesions (critical stenosis and occlusion). This method will also provide a means of quantitatively evaluating changes induced in the vasculature by natural history of the disease or surgical therapy. Experiments will be carried out in flow models, animals and non-invasive measurements will be made in humans. These experiments will be correlated with clinical and angiographic data. Velocity waveforms will be sensed trans-cutaneously. By Real-Time Spectrum Analysis of C.W. Doppler ultrasound, the following parameters will be determined: transit time (t) a measure of the pulse propagation velocity, damping delta an indicator of the amount of velocity waveform modification caused by the presence of plaques and/or collaterals, and quantification of changes in velocity wave shapes. From these parameters it will be possible to determine (1) the elastic condition of the vessel wall, (2) the presence or absence of a stenosis or occlusion, (3) the degree of stenosis and (4) the size of the collateral bed.